Medication delivery pens are hypodermic syringes used for self-injection of precisely measured doses of medication. Pens are widely used, for example, by diabetics to self-inject insulin. A typical prior art medication delivery pen includes a cartridge which contains a volume of liquid medication sufficient for several doses. The dose is injected into a tissue area, such as the intramuscular tissue layer, the subcutaneous tissue layer, or the intradermal tissue layer.
The assembly and operation of a typical pen injection device is described in commonly-assigned U.S. Pat. No. 7,645,264, issued on Jan. 12, 2010, which is incorporated herein by reference in its entirety.
Pen injection devices, such as the exemplary pen injector 50, as shown in FIGS. 1 and 2, typically comprise a dose knob/button 24, an outer sleeve 13, and a cap 21. The dose knob/button 24 allows a user to set the dosage of medication to be injected. The outer sleeve 13 is gripped by the user when injecting medication. The cap 21 is employed by the user to securely hold the pen injector 50 in a shirt pocket, purse, or other suitable location.
FIG. 2 is an exploded view of the exemplary drug delivery pen 50 shown in FIG. 1. The dose knob/button 24 has a dual purpose and is used to both set the dosage of the medication to be injected and to inject the dosed medicament via a lead screw 7 and stopper 15 from a medicament cartridge 12, which is attached to the drug delivery pen through a lower housing 17. The lower housing 17 typically has dosage indicia on the exterior thereof. The medicament cartridge 12 is typically a glass tube sealed at one end with a septum 16 and at the other end with the stopper 15. In standard drug delivery pens, the dosing and delivery mechanisms are all found within the outer sleeve 13. Those mechanisms are not described in greater detail here as they are understood by those knowledgeable of the art.
A pen needle 10 includes a hub 20, a patient needle 11 extending from a patient end of the pen needle, and a septum-penetrating needle cannula 18 disposed within the hub 20 on a non-patient side thereof. The septum-penetrating needle cannula 18 is in fluid communication with the patient needle 11. The hub 20 is preferably screwed onto the lower housing 17. In attaching the hub 20 to the lower housing 17, the septum-penetrating cannula 18 pierces the septum 16, but the septum 16 does not move with respect to the medicament cartridge 12. The stopper 15, however, is axially displaceable within the medicament cartridge 12 while maintaining a fluid tight seal. The distal movement of the plunger or stopper 15 within the medicament cartridge 12 (due to advancement of the lead screw 7) causes medication to be forced into the patient needle 11 of the hub 20.
To protect a user, or anyone who handles the pen needle assembly 10, an outer shield 29, which attaches to the hub 20, covers the hub 20. The outer shield 29 can also be used as a handle or grip to screw hub 20 onto or off pen injector 50. An inner shield 28 covers the patient needle 11 within the outer shield 29. The inner shield 28 can be secured to the hub 20 to cover the patient needle 11 by any suitable means, such as an interference fit or a snap fit. The outer shield 29 and inner shield 28 are removed prior to use. The cap 21 fits snugly against outer sleeve 13 to allow a user to securely carry the pen injection device 50.
FIG. 3 is a cross-sectional view of an exemplary cartridge 76 and a lower housing or cartridge retainer 78 for a drug delivery pen, such as the pen injector 50. As shown in FIG. 3, opposing ends of cartridge retainer 78 include threads 80 and 82 for respectively connecting the cartridge retainer 78 to pen needle assembly 10 and the outer sleeve 13. The lower housing 80 may be made of, for example, plastic. The cartridge 76 may be made of, for example, glass.
A stopper 84 is movably disposed within an interior cavity of the cartridge 76. The stopper 84 is shown in phantom lines in a position for the beginning of an injection, and is shown in cross section in a position representing the end of the useful life of the cartridge 76. In other words, no more medicament 86 can be ejected from the cartridge 76. More specifically, the leading surface of the stopper 84 forms a substantially right angle with the side thereof. And during blowing or other elongation of the glass to form the cartridge 76, an end 88 of the interior cavity of the cartridge is radiused. Therefore, the stopper 84 can only be moved a certain distance in the interior cavity before the radius of the end 88 prevents further movement of the stopper 84. Accordingly, an uninjectable, or dead volume of medicament remains in the cartridge 76.
A septum 92 is held on the end of the cartridge 76 by a crimping ring or band of metal 94. The septum 92 is made of, for example, rubber and the crimping ring 94 is made of, for example, aluminum or plastic. During installation of the septum 92 and crimping of the crimping ring 94, particles from the septum 92 and/or the crimping ring 94 may be generated and may enter the interior cavity of the cartridge 76.